Question: Solve for $b$. $-3b+2.5 = 4$
Answer: Let's subtract and then divide to get $b$ by itself. $\begin{aligned} -3b+2.5& = 4 \\ \\ -3b+2.5 {-2.5}&= 4{-2.5}~~~~{\text{subtract }2.5} \text{ from each side}\\ \\ -3b+\cancel{ 2.5} {{-}\cancel{{2.5}}}&= 4{-2.5}\\ \\ -3b &=4{-2.5}\end{aligned}$ $\begin{aligned}-3b &= 1.5 \\ \\ \dfrac{-3b}{{-3}} &= \dfrac{1.5}{{-3}} ~~~~~~~\text{divide each side by } {-3} \text{ to get } b \text{ by itself }\\ \\ \dfrac{\cancel{-3}b}{\cancel{{-3}}} &= \dfrac{1.5}{{-3}} \\ \\ b &= \dfrac{1.5}{{-3}} \end{aligned}$ The answer: $b={-0.5}$ Let's check to make sure. $\begin{aligned} -3b+2.5 &= 4 \\\\ -3({-0.5})+2.5 &\stackrel{?}{=} 4 \\\\ 1.5+2.5 &\stackrel{?}{=} 4 \\\\ 4 &= 4 ~~~~~~~~~~\text{Yes!} \end{aligned}$